The mechanical behaviour of a reconstituted unsaturated silty clay

Abstract

This paper describes a novel method of controlling suction by means of air circulation in combination with independent suction measurement. The technique has been incorporated in a standard triaxial stress path cell, and could easily be incorporated in other standard apparatus such as the direct shear box and oedometer. The application of the technique is demonstrated by means of an exploratory testing programme in which samples of a reconstituted saturated clayey silt were progressively dried to various predetermined suctions, which were then maintained constant during isotropic compression followed by shearing to failure. In this way the drying and stress history of the soil was carefully controlled in a way that could be made representative of the genesis of natural unsaturated soils. Though exploratory, the experimental investigation described in this paper has provided some interesting and thought-provoking results. Prior to desaturation the clayey silt behaves in accordance with the classical critical-state framework, even under suctions as high as 400 kPa. Once desaturation occurs, important changes in behaviour take place. In particular, the behaviour changes from being ductile to very brittle in a way that is difficult to account for within the critical-state framework. The new technique provides a ready means of carrying out detailed studies of the influence of various combinations of changes in suction and applied stress on a wide range of soil types and in a variety of apparatus.